Most cosmetic or dermatopharmaceutical products designed for topical application--whatever the galenic form: H/E, E/H emulsion, milk, lotion, gel, solution--contain one or more microbicidal substances in their formulation. The reasons for this are obvious: the raw materials used for the manufacture of these products are only rarely perfectly sterile, the finished products are too fragile (perfume, biologically active compounds, vitamins) to uphold sterilization following conditioning. It is thus necessary to protect the product from any microbial contamination which could be detrimental to the health of the user or to the aesthetic appearance of the product. This contamination can arise from the manufacturing process (including the raw materials used), from a packaging that is not hermetically sealed and above all following opening, from the environment or the user himself.
In contrast to food products or to pharmaceutical products, cosmetic products are not required to exhibit an expiration date; they can and must therefore be stable and in perfect condition--including microbiologically--for a long time.
The chemical preservatives used in these products fulfil this protective role. The choice of antimicrobial substances or biocidal molecules being used is strictly controlled by the different legislation of European, American and Asian countries.
Since to be effective all preservative must be chemically active, destroying either the cellular wall or the biochemical mechanisms of microbial cells, it is not surprising that these same biocidal molecules sometimes have a detrimental effect on the human cells with which they come into contact. It is a fact that with the increased use of cosmetic or dermatopharmaceutical products, a parallel increase in cases of intolerance (irritation, allergy) to these products has been observed. The studies performed by various dermatologists, pharmacists or health authorities reveal that a number of these incidents can be attributed to the preservatives contained in the products.
Moreover, the ecological trend of our time reinforces the desire of the cosmetic industry to offer "natural", "mild" or "hypoallergenic" products. Means of protecting the creams without the incorporation of preservatives are been sought.
The formulation of cosmetic products without preservatives is however not easy. It is presently possible, using selected, sterile raw materials and ensuring manufacture under strict aseptic hygiene conditions (conditioning under laminar flow into sterile containers). Remains the risk of contamination during use. Only the choice of a specific packaging, designed to deliver the dose for use at the time of application, and preventing any entry of air and germs inside the container, can satisfy these constraints.
As a result, the diversity of the ranges of cosmetic products that can be prepared without preservative is limited, and above all the cost of manufacture and conditioning is significantly increased.
Patent FR 2 682 296 proposed a non-chemical method of preservation that is based on the use of gels of the glyceryl poly(meth)acrylate type, the property of which is to exert a strong osmotic effect on its environment, making it possible to inactivate the microorganisms introduced into the cosmetic preparation through water deprivation. Microbiological tests of overcontamination (for example, the inoculation of 10.sup.6 germs/gram of a cream containing 40% of the gel in question is controlled in 7 days only when the gel is present in the formulation, in the absence of any chemical preservative) have been able to demonstrate this antimicrobial efficacy of the gel. The method described in this patent has proven applicable in practice, but it has a number of disadvantages: the amount of gel required in a cosmetic formulation is very high (minimum 40% in the best cases; often the gel must be incorporated at the rate of 30%, even 60%). This limits the field of application, as the formulator is subjected to constraints in his freedom to adapt the texture, the touch of the products. Another disadvantage came out of successive testing: protection of the finished products to contamination by particular moulds (ex: Aspergillus niger) is very difficult to achieve, this germ requiring very little free water for its growth; it is therefore less sensitive to the water deprivation brought about by the gel.